Subscriber station transceiver allocation of groups of subcarriers between a plurality of transceiver antennas

ABSTRACT

Embodiments for at least one method and apparatus of a subscriber station transceiver allocating and transmitting groups of subcarriers between a plurality of transceiver antennas are disclosed. One method includes the subscriber station transceiver receiving at least one downlink signal through each of the plurality of subscriber station antennas. The subscriber station transceiver characterizes a received signal of the at least one downlink signal over multiple subcarriers. The subscriber station transceiver allocates groups of subcarriers for uplink transmission through each of the plurality of subscriber antennas, wherein the allocation is based on the characterized received signal of the at least one downlink signal over multiple subcarriers.

RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional ApplicationNo. 61/194,846, filed Oct. 1, 2008, and herein incorporated byreference.

FIELD OF THE DESCRIBED EMBODIMENTS

The described embodiments relate generally to wireless communications.More particularly, the described embodiments relate to allocating groupsof subcarriers between a plurality of antennas of a transceiver.

BACKGROUND

Wireless networks are gaining popularity because wirelessinfrastructures are typically easier and less expensive to deploy thanwired networks. A popular wireless network implementation uses basestations that communicate with wireless user devices that are locatedwithin cells formed by the base stations.

The wireless user devices are commonly referred to as wirelesssubscriber stations. A wireless subscriber station commonly employs asingle antenna. Configuring the subscriber station to have multipleantennas can be beneficial because intelligent multiple antennatransmission schemes (such as spatial multiplexing) can be utilized.However, transmission from multiple antennas may require adjustment of aphase between the transmission signals, which in some cases can bedifficult to implement.

It is desirable to have a method of optimizing uplink transmission ofsubscriber station transceivers using multiple antennas.

SUMMARY

An embodiment includes a method of a subscriber station transceiverallocating and transmitting groups of subcarriers between a plurality oftransceiver antennas. The method includes the subscriber stationtransceiver receiving at least one downlink signal through each of theplurality of subscriber station antennas. The subscriber stationtransceiver characterizes a received signal of the at least one downlinksignal over multiple subcarriers. The subscriber station transceiverallocates groups of subcarriers for uplink transmission through each ofthe plurality of subscriber antennas, wherein the allocation is based onthe characterized received signal of the at least one downlink signalover multiple subcarriers.

Other aspects and advantages of the described embodiments will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a base station and a subscriber stationtransceiver, wherein multiple propagation channels are formed between abase station antenna and each subscriber station antenna.

FIG. 2 shows an example of a block diagram of subscriber stationtransceiver employing multiple antennas.

FIG. 3 shows a flow chart that includes steps of an example of a methodfor assigning groups of adjacent subcarriers to each of a plurality ofantennas.

FIG. 4A shows an example of a group of subcarriers that includes pilotsubcarriers and data subcarriers over multiple multi-carrier symbols.

FIG. 4B shows another example of a group of subcarriers that includespilot subcarriers and data subcarriers over multiple multi-carriersymbols.

FIG. 5 shows an example of six groups of subcarriers over multiplesymbols.

FIG. 6 shows an example of groups of subcarriers that have beenallocated between two subscriber station antennas.

FIG. 7 shows an example of measurements taken over a range offrequencies of the downlink signals, and the corresponding allocating ofgroups of subcarriers between two subscriber station antennas, based onthe measurements.

FIG. 8 shows a flow chart of steps of an example of a method of asubscriber station transceiver allocating and transmitting groups ofsubcarriers between a plurality of transceiver antennas.

DETAILED DESCRIPTION

The embodiments described include methods and apparatuses of asubscriber station transceiver allocating and transmitting groups ofsubcarriers between a plurality of transceiver antennas. The allocationand transmission does not require control and/or adjustment of the phasebetween multiple transmission signals.

FIG. 1 shows an example of a base station 110 and a subscriber stationtransceiver 120, wherein multiple propagation channels H₁, H₂, areformed between each base station antenna 112 and each subscriber stationantenna 122, 124. It is to be understood, however, the base station 110can include multiple antennas, and the subscriber transceiver 120 caninclude more than two antennas.

A wireless communication signal traveling from the base station 110 tothe subscriber station 120 is typically referred to as “downlinktransmission”, and a wireless communication signal traveling from thesubscriber station 120 to the base station 110 is typically referred toas “uplink transmission”. The transmissions can be included within aframe that includes a downlink sub-frame and an uplink subframe.

Some embodiments include the base station of the wireless systemscheduling the wireless communication and the scheduling is communicatedto subscriber stations through a control channel. The control channelcan provide scheduling allocations, which for a multi-carrier system(such as an orthogonal frequency division multiplexing (OFDM)),designates sub-carriers and time intervals in which downlink and uplinktransmissions between the base station and each mobile subscriber are tooccur.

The control channel may be transmitted to the subscriber station withina downlink sub-frame. Embodiments of the downlink sub-frame mayadditionally include a preamble. The preamble can occur at the beginningof every frame. Embodiments of the preamble include pilot tones(generally referred to as pilots) being closely spaced across carriersof a multi-carrier signal. For example, one embodiment includes thepilots being occurring every third tone across the frequency spectrum ofa multi-carrier signal. The pilots in the preamble can be transmitted ata higher power spectral density and contain modulation known to thereceiver (subscriber station) as compared to data carrying subcarriers.These pilots can be used by communication systems to estimate thechannel and/or to correct frequency and timing offsets.

For descriptive purposes, the down link channel as shown can berepresented by:

$\begin{matrix}{H_{DL} = {\begin{bmatrix}H_{1} \\H_{2}\end{bmatrix}.}} & (1)\end{matrix}$where H_(DL) is the downlink (DL) propagation channel. The signalreceived by the SS can be given by:y _(SS) =H _(DL) s _(DL) +n∈

,  (2)where s_(DL) denotes the signal transmitted by the base station, n∈

is the additive noise plus interference, and

 denotes the field of complex numbers. In practice, the downlinktransmission is often transmitted from more than one antenna using avirtualizing scheme, such as, Cyclic Delay Diversity (CDD). In thiscase, the signals received by the subscriber appear to have beentransmitted by a single virtual antenna.

The received uplink (UL) signal can be represented byy _(BS) =H _(UL) s _(UL)+η∈

,  (3)where s_(UL)∈

denotes the signal transmitted by the two antennas 122, 124 at thesubscriber and η∈

denotes the additive noise present on the received UL signal.

For a time division duplex (TDD) system, the SS may exploit thereciprocity of the channel. More specifically:H _(UL)(t)≅H _(DL) ^(T)(t+T),  (4)provided J₀(2πDT)≅1, where D is the Doppler spread of the propagationchannel, J₀(·) denotes the zero order Bessel function of the first kind,and T is the time duration between when the downlink channel wasestimated and when the UL signal is transmitted.

One example of a communication system includes a WiMAX (WorldwideInteroperability for Microwave Access) system. WiMAX systems includemulti-carrier, OFDM (Orthogonal frequency-division multiplexing)signals. A WiMAX transceiver may include a baseband digital signalprocessor which outputs two baseband signals (the described embodimentsare not limited to two output baseband signals), possibly complex. Thesebaseband output signals are up-converted in frequency and applied to twopower amplifiers. The outputs of the power amplifiers are connected totwo antennas (again, the described embodiments are not limited to twoantennas) which are used for both transmit and receive. Each means forup-converting the baseband signals and amplifying them can be referredto as a transmit chain. The need for two transmit chains arises from therequirement to transmit a space-time block code or to transmit multiplespatial streams (spatial multiplexing). In WiMAX, the space time blockcode may be the Alamouti code, which is commonly referred to as MatrixA. In the same context, spatial multiplexing is commonly referred to asMatrix B.

In addition to transmitting Matrix A and Matrix B, it is attractive toexploit the available transmit power of both power amplifiers whentransmitting a single spatial stream; hence, improving the quality ofthe uplink signal as received by the base station.

Consider, for example, a subscriber station in which an RF signal isapplied to an RF signal is applied to a first antenna element and aphase-shifted version of the same RF signal is applied to a secondantenna element. The resulting far-field radiation pattern depends onthe geometry of the antenna elements and the phase shift of the signalapplied to the second antenna element. If the relative phases of thesignals at the two antennas are not carefully controlled, the benefit oftransmitting the signal from a second antenna may not accrue; worsestill, the signals may combine destructively. Hence, the method oftransmitting the same RF signal from a plurality of antennas withoutcontrolling the relative phases of the applied RF signals is notattractive.

Two methods have been used to avoid this problem. The first, (cyclicdelay diversity) CDD, applies a frequency dependent phase shift to avoiddestructive cancellation of the signals across all frequencies. Thesecond method, Tile Switching Diversity (TSD) varies transmit antennas,but does not make use of the relative strengths of the received signalsfor assignments of groups of subcarriers. Both CDD and TSD aresuboptimal methods as they fail to exploit the subscriber station'sknowledge of and the reciprocity of the channel.

It is desirable to use the available power from two power amplifiers inthe two transmit chains without controlling the phase of the signalsapplied to each of the antennas. It is also desirable to exploit thesubscriber stations knowledge of the UL channel.

In the embodiment disclosed, the subscriber transmits constituentspectral components of an UL signal from one of the two availableantennas. Therefore, the transmitted spectral components arenon-overlapping between the antennas. This precludes the problemsassociated with transmitting a common RF signal from two antennaswithout controlling the phases. These spectral components are groupedinto blocks of subcarriers.

The available output power of the power amplifiers (PAs) may constrainthe number of subcarriers that can be transmitted at a desired powerspectral density. Embodiments include assigning groups of subcarriersfor transmission from each antenna to maximize a UL link quality,subject to the power constraints of the power amplifiers (PAs). Theobjective of maximizing the UL link quality is based on maximizing anobjective function of the expected UL channel. A recently estimated DLchannel can be used as a proxy for the UL channel in an upcoming ULtransmission. This downlink channel estimate may be formed, for example,from the preamble of a frame of the downlink signal. Alternativelyand/or additionally, the downlink channel estimate can be derived basedon pilots that occur after the preamble in the DL subframe.

Embodiments include transmitting the UL signal transmissions on exactlyone of the UL antennas to maximize capacity or its proxy SNR, subject tothe power constraints of the PAs.

At the BS, the receive signal processing includes estimating the ULchannel. This channel estimation commonly averages the pilots of a groupof adjacent subcarriers for the purpose of reducing the effects ofadditive noise and interference. In general, the channels from thesubscriber station antennas to the BS antennas are different in bothamplitude and phase. To preclude introducing channel estimation errorsdue to averaging at the base station, embodiments include avoiding theseparation of tiles across subscriber antennas. For the WiMAX system, auseful grouping of subcarriers includes, for example, PUSC UL tiles,wherein PUSC refers to the Partial Usage of Subchannels.

It is advantageous to assign groups of subcarriers on a tile-by-tilebasis for two reasons. First, the UL tiles span a narrow range offrequencies. Therefore, the channel typically varies by only a smallamount across the tile and the channel for all subcarriers within thisgroup can be effectively characterized by a single metric.

Second, the collection of tiles that make up a subchannel do not changeduring the UL subframe. This allows us to assign tiles to individualantennas without concern that subsequent assignment, on subsequentsymbols, may result in the same tile being transmitted on differentantennas on different symbols. This is true even in the case of, forexample, subchannel rotation in, WiMAX systems. Subchannel rotation isdescribed in section 8.4.6.2.6 of the IEEE 802.16 standard.

Other useful grouping of subcarriers include the Band AMC bin in theWiMAX standard and the Physical Resource Block (PRB) in the 3rdGeneration Partnership Program Long-Term-Evolution (LTE) standard.

FIG. 2 shows block diagrams of an example of radio frequency (RF)transmission chains associated with each antenna of the subscriberstation transceiver. For this example, of the transmitter component ofan OFDM transmitter used in a mobile station (MS). The symbol data (forexample, Data 1 which processed through a transmitter chain 1 beforetransmission from the first antenna Ant. 1) is applied an input IFFTcircuit 210 which implements an inverse Fast-Fourier transform (IFFT).The real and imaginary (I, Q) components of the IFFT outputs areupsampled by upsamplers 212 a and 212 b, which interdigitate zerosbetween the samples of the IFFT output. The upsampled signals are passedthrough digital lowpass filters 214 a, 214 b, digital-to-analogconverters (DACs) 216 a, 216 b, analog lowpass filters 218 a, 218 b,before being frequency upconverted and combined by an RF upconverter220. The frequency upconverted signal is amplified by a power amplifier230 and transmitted from the first antenna Ant. 1. The other transmitchain (transmit chain 2) includes similar functional blocks as the firsttransmit chain (transmit chain 1), including a power amplifier 232.

Switches 240, 242 generally provide switches connections between the twoantennas Ant. 1, Ant. 2 and the transmit chains 1, 2 and the receiverchains 1, 2.

The receive chains (receive chain 1, receive chain 2) include RFfrequency downconverters, frequency translators, analog lowpass filters,analog to digital converters (ADCs) and signal processors. The receivechains generate received baseband signals, and with signal processing,generate Data, and the channel estimates (for example, vectors Ĥ₁ andĤ₂).

FIG. 3 shows a flow chart that includes steps of an example of a methodfor assigning groups of adjacent subcarriers to each of a plurality ofantennas. Mutually exclusive assignments (allocations) of groups ofsubcarriers can be made to preclude the additional directivityassociated with transmitting a signal component from a first antenna anda potentially phase shifted version of the signal component from asecond antenna. Let ƒ∈

denote the center frequencies of the groups of subcarriers to betransmitted on the uplink, where

 denotes the field of real numbers. Let H ₁ ∈

and H ₂ ∈

be the vectors of estimated values of received DL channels at thesubscriber station antennas 1 and 2, respectively, where H ₁(i)=Ĥ₁(ƒ(i))and H ₂(i)=Ĥ₂(ƒ(i)). Let q₁:

→

and q₂:

→

be real, vector valued functions of the received downlink channelmeasurements at frequencies ƒ(1) . . . ƒ(M). Functions q₁(·) and q₂(·)correspond to expected utility of transmitting the groups of subcarrierson antennas 1 and 2, respectively.

Let Q:

×

×{0,1}^(M)→

denote the functionalQ( H ₁ ,H ₂ ,k)=k ^(T) q ₁( H ₁)+(1^(T) −k)q ₂( H ₂),  (5)where k∈{0,1}^(M) denotes a vector of binary decisions, 1 denotes an Mdimensional (column) vector of ones, and (·)^(T) denotes transpose.Here, elements of k define the decisions for allocating thecorresponding groups of subcarriers to antennas 1 and 2. A value of 1indicates that the corresponding group of subcarriers is assigned toantenna 1; a value of 0 indicates assignment to antenna 2.

It is desirable to transmit the various UL times on exactly one of theUL antennas (Ant. 1, Ant. 2) to maximize the overall utility function,as shown in Equation (5), subject to the per-antenna power constraint.

A useful choice for functions q₁(·) and q₁(·) are the received downlinksignal powers estimated at the frequencies at which the groups of ULsubcarriers are to be transmitted. That is, by:q ₁ =|H ₁|²∈

  (6)andq ₂ =|H ₂|²∈

.  (7)Another choice for functions q₁(·) and q₁(·) are given by the expectedcapacities of the UL channels, viz.,

$\begin{matrix}{q_{1} = {{\log_{2}\left( {1 + \frac{{{\underset{\_}{H}}_{1}}^{2}}{\sigma_{1}^{2}}} \right)} \in {\left\{ {\mathbb{R}}^{+} \right\}^{M}.{and}}}} & (8) \\{{q_{2} = {{\log_{2}\left( {1 + \frac{{{\underset{\_}{H}}_{2}}^{2}}{\sigma_{2}^{2}}} \right)} \in \left\{ {\mathbb{R}}^{+} \right\}^{M}}},} & (9)\end{matrix}$where σ₁ and σ₂ denote the, potentially unknown, noise plus interferenceat the base station. For σ₁=σ₂, the capacity metrics in (8) and (9) arewell approximated by the signal power metric in (6) and (7) as log₂(1+x)≅log₂(e)·x for x small. The use of signal strength affords theadditional benefit of reduced computational complexity.

Yet another choice for functions q₁(·) and q₁(·) is given byq ₁=(| H ₁|² +|H ₂|²)∘I(| H ₁|² −|H ₂|²)∈

.  (10)andq ₂=(| H ₁|² +|H ₂|²)∘I(| H ₂|² −|H ₁|²)∈

,  (11)where ∘ denotes the Hadamard or element-wise product and I(·):

→{0,1}^(M) is a vector valued indicator function with for which

$\begin{matrix}{{I_{k}(x)} = \left\{ {\begin{matrix}1 & {x_{k} \geq 0} \\0 & {{else}.}\end{matrix},} \right.} & (12)\end{matrix}$where x∈

and x_(k) denotes the k^(th) element of x. This choice of functionscorresponds to a binary decision weighted by sum of the signal powersreceived by the two antennas.The gradient of the objective function Q in equation (5) is given by:

$\begin{matrix}{g = {\frac{\partial Q}{\partial k} = {{q_{1} - q_{2}} \in {{\mathbb{R}}^{M}.}}}} & (13)\end{matrix}$Power amplifiers typically have a maximum rated output power, beyondwhich, they distort causing out-of-band emissions or an increase inerror vector magnitude (EVM). When transmitting at maximum, or nearmaximum power, this may constrain the maximum number of groups ofsubcarriers that can be transmitted from a single antenna. Let m ₁ and m₂ denote the maximum number of groups of subcarrier can be transmittedfrom antenna 1 and antenna 2, respectively. Additionally, it can beassumed that each group of subcarriers must be transmitted from at leastone of the antennas. Therefore, the assignment of the groups ofsubcarriers can be viewed as be following optimization problem:Q*=max k ^(T) q ₁−(1^(T−) k)q ₂ s.t. M− m ₂≦1^(T) k≦ m ₁,k∈{0,1}^(M)  (14)The affine dependence of the objective may be used to efficiently solvefor the optimal decision vector k*, wherek*=arg max k ^(T) q ₁−(1^(T) −k)q ₂ s.t. M− m ₂≦1^(T) k≦ m ₁,k∈{0,1}^(M)  (15)

Given a strictly feasible constraints m ₁ and m ₂ with m ₁+ m ₂≦M and agradient of the objective function, g∈

, we can solve for the vector of optimal assignments k∈{0,1}^(M) usingan algorithm, for example, as shown in FIG. 3. For the purpose ofexplaining the algorithm, consider that creation of a sequence ofindices n=[n₁ . . . n_(M)] such that with s(i)=g(n_(i)) withs(i)≧s(i+1)∀i∈[1,M−1]. This sequence could be obtained by sorting theelements of g in descending order. The full sorting of g is notnecessary as shown below.

A step 310, of FIG. 3, includes forming an initial assignmentk ₀ =I(g)∈{0,1}^(M),  (16)where I(·)∈{0,1}^(M) is as defined in (12).

A Step 320 includes computing cardinality of initial assignmentsaccording to m₀=1^(T)k₀.

A Step 330 evaluating a sum constraintm₀≦ m ₁.  (20)

If the constraint is met, go to step 360; otherwise, determine the m₀− m₁ indices smallest entries of g having a nonnegative sign as describedin Step 340. Denote these indices as n _(m) ₁ ₊₁ . . . n_(m) ₀ . Notethat that determination of these indices requires less computationaleffort than a full sorting of the gradient vector g. The interpretationis to identify the indices that allow meeting the sum constraint in (20)with minimal effect to the objective function. The gradients as definedin (13) give the sensitivity of the objective function (5) tomodification of the elements of k₀. These sensitivities correspond toLagrange multipliers or the shadow prices associated with the per-PApower constraint.

A Step 350 includes assigning the groups of subcarriers according to thedecision vector k*, with k*(n_(i))←1, ∀i=1 . . . m ₁ and k*(n_(j))←0,∀j= m ₁+1 . . . M.

A Step 360 includes evaluating a sum constraintM−m ₀ ≦ m ₂.  (17)If constraint is met, the initial assignment of k₀ is optimal and k*←k₀.Otherwise, a Step 370 includes determining the M−m₀− m ₂ indices of thenegative entries of g having the smallest absolute value as described inStep 340. These indices can be denoted as n_(m) ₀ ₊₁ . . . n_(M− m) ₁ .As before, determining these indices requires less computationalcomplexity than the complete sorting of the gradient vector g.

A Step 380 includes assigning the groups of subcarriers according to thedecision vector k*, with k*(n_(i))←1, ∀i=1 . . . M− m ₂ and k*(n_(i))←0,∀j=M− m ₂+1 . . . M.

If the power amplifiers associated with antenna 1 and antenna 2 arecapable of producing the same output power, the maximum number of tilesto transmit from each antenna is the same; that is, m ₁= m ₂.

The example of FIG. 3 corresponds to a method for assigning groups ofadjacent subcarriers based on downlink channel quality metrics subjectto meeting transmit power constraints of the subscriber stationtransceiver.

FIG. 4A shows an example of a group of subcarriers (for example a WiMAXPUSC-tile) that includes pilot subcarriers and data subcarriers overmultiple multi-carrier symbols. The PUSC-tile of FIG. 4A includessubcarriers that are defined by subcarriers locations k+1, k+2, k+3, k+4and by OFDM symbol numbers 1, 2, 3. The tile shown includes pilots atthe corners of the tile, and data subcarriers in the remaininglocations.

FIG. 4B shows another example of a group of subcarriers that includespilot subcarriers and data subcarriers over multiple multi-carriersymbols. This embodiment is consistent with Band_AMC of the WiMAXstandard.

FIG. 5 shows an example of a subchannel that includes six groups ofsubcarriers over multiple symbols. Each of the tiles includes pilot anddata subcarriers which are the same as the tile shown in FIG. 4A. For atleast some embodiments, the six tiles constitute a subchannel. The sixtiles of the subchannel have been labeled ƒ_(j)(1), ƒ_(j)(2), ƒ_(j)(3),ƒ_(j)(4), f_(j)(5), ƒ_(j)(6). Here, j denotes the subchannel index.

FIG. 6 shows an example of tiles (groups of subcarriers) that have beenallocated between two separate subscriber station transmit antennas. Asshown, each antenna (Ant. 1, Ant. 2) have been allocated three out of apossible six tiles. Also as shown, none of the allocated tiles of oneantenna overlap in frequency with the allocated tiles of the otherantenna. That is, tiles ƒ_(j)(1), ƒ_(j)(4), ƒ_(j)(6) have been allocatedto the antenna Ant. 1 and tiles ƒ_(j)(2), ƒ_(j)(3), ƒ_(j)(5) have beenallocated to the other antenna Ant. 2. All of the tiles are allocated toa single antenna. Any of the described embodiments can be used formaking the tile allocations between the two antennas. As previouslydescribed, the allocations can be over more than two antennas, and caninclude any number of tiles.

FIG. 7 shows an example of channel measurements taken over a range offrequencies of the downlink signals, and the corresponding allocating ofgroups of subcarriers (tiles) between two separate subscriber stationantennas, based on the channel measurements. That is, channelmeasurements are made at both antennas (Ant. 1, Ant. 2) before theallocating the tiles to the antennas. The measurements can be made, forexample, during a preamble of a downlink sub-frame. As shown, themeasurements are made over each of six intervals (Interval 1, Interval2, Interval 3, Interval 4, Interval 5, Interval 6) on both of theantennas. Based on the measurements, the groups of subcarriers (tiles)are allocated between the two antennas (Ant. 1, Ant. 2). As shown, noneof the allocated tiles of one antenna overlap in frequency with theallocated tiles of the other antenna. As shown in FIG. 7, themeasurements of the DL channel can be made over intervals in frequencythat correspond to the frequencies of the tiles to be allocated for ULtransmission. An embodiment includes measuring the DL channel over aninterval in frequency that overlaps the frequencies of the tiles to beallocated for UL transmission. Another embodiment includes measuring theDL channel at a frequency in the interval of the frequencies of thetiles to be allocated for UL transmission. An alternate embodimentincludes measuring the DL channel at a plurality of frequencies andmaking the allocation of tiles for UL transmission based on thesemeasurements.

FIG. 8 shows a flow chart of steps of an example of a method of asubscriber station transceiver allocating and transmitting groups ofsubcarriers between a plurality of transceiver antennas. A first step810 includes the subscriber station transceiver receiving at least onedownlink signal through each of the plurality of subscriber stationantennas. A second step 820 includes the subscriber station transceivercharacterizing a received signal of the at least one downlink signalover multiple subcarriers. A third step 830 includes the subscriberstation transceiver allocating groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennas,wherein the allocation is based on the characterized received signal ofthe at least one downlink signal over multiple subcarriers.

An embodiment includes the subscriber station characterizing the receivesignal based on a received signal power. Further, the groups ofsubcarriers are allocated based on the received signal power. Forexample, characterizing the received downlink signals can includedetermining a relative signal power difference between multiplesubcarrier signals received through each of the plurality of subscriberantennas. The received signal power for each antenna of the subscriberstation can be determined by measurement at the subscriber station.

An embodiment includes allocating the groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennas basedon an expected uplink channel quality as estimated based on thecharacterized received signals of the at least one downlink signal oversubcarriers. For one embodiment, the expected uplink channel quality isbased on at least one of an expected uplink capacity, an expected uplinksignal-to-noise ratio (SNR), an expected uplink signal-to-interferenceand noise (SINR), expected uplink total received signal power. Foranother embodiment, the expected uplink channel quality is based on atleast one of an estimated downlink capacity, an estimated downlinkreceived signal power.

The SNR can be estimated at the subscriber station using knowledge ofthe preamble and/or pilot subcarriers. The estimated SNR can be used toestimate the expected capacity C, using the relationship C=log₂(1+SNR).

Another embodiment includes allocating groups of subcarriers based on atleast one of a sum of receive signal powers across the plurality ofsubscriber station antennas, a sum signal-to-noise ratios across theplurality of subscriber antennas, a weighted sum of signal-to-noiseratios across the plurality of subscriber antennas. The weighting can bedependent on a long term average received signal power, and/or resultsfrom a factory calibration.

Another embodiment includes the subscriber station transceivercharacterizing the received downlink signals based on subcarrierscorresponding to the groups of subcarriers to be transmitted on theuplink. That is, the groups of subcarriers (for example, tiles) may havebeen designated, for example, by a base station. The base stationdesignation can include the designation of specific multi-carriersubcarriers. This embodiment includes the characterizing of the receiveddownlink signals based on subcarriers occurring on the samecorresponding groups of subcarriers (tiles) as designated by the basestation.

For another embodiment, the subscriber station transceivercharacterizing a received signal power of the at least one downlinksignal over multiple subcarriers includes characterizing pilot tones ofa preamble of a downlink sub-frame of the at least one downlink signal.For example, the subscriber station transceiver characterizes the DLchannel, using pilot tones of the preamble, corresponding to the groupof subcarriers to be allocated on the uplink. Alternatively thesubscriber characterizes the received signal of the at least onedownlink signal over at least one subcarrier that occur over a range ofsubcarriers that overlap the group of subcarriers to be allocated on theuplink. Alternatively, the subscriber characterizes the received signalof the at least one downlink signal that includes at least onesubcarrier that occurs within the range of subcarriers as the group ofsubcarriers to be allocated on the uplink. Alternately, the subscribercharacterizes the received signal of the at least one downlink signalover at least one subcarrier that occur over a range of subcarriers thatoverlap the group of subcarriers to be allocated on the uplink.Alternatively, the subscriber characterizes the received signal of theat least one downlink signal at a plurality of frequencies.Additionally, or alternatively, pilots that are not within the preamblecan be characterized.

An embodiment includes the subscriber characterizing the downlinkreceived signals over a plurality of frames. For example, the downlinkreceive signals are characterized during the preamble of severalsuccessive downlink sub-frames. The averaging is done to reduce theimpact of estimation error on the characterization of the downlinkreceived signals.

An embodiment includes allocating groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennas bysorting a difference of vector of downlink channel quality metrics fromthe plurality of subscriber station antennas. A more specific embodimentincludes performing initial allocations based on the sorted differencevector of downlink channel quality metrics, determining a number ofgroups of subcarriers allocated to each subscriber antenna, andmodifying the initial allocations of groups of subcarriers to meettransmit power constraints of the subscriber station transceiver whilecausing minimal change to the expected UL quality metric.

An embodiment includes allocating groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennas bysorting of a gradient of a downlink channel quality figure of merit(gradient of Q) based on the received downlink signals.

Another embodiment includes the subscriber characterizing the receivedsignal power of the downlink signals over multiple subcarriers byfiltering the downlink channel estimates to reduce the impact of channelestimation errors.

Another embodiment includes allocating groups of subcarriers within atleast one sub-channel of multiple sub-channels. The allocation based ona sub-channel is done to reduce the computational complexity of theallocation process at the subscriber station. An embodiment includesallocating groups of subcarriers such that the allocations of the tilesto antennas are maintained for a time interval greater than the minimumtime interval of the groups of allocated subcarriers during an ULtransmission. A WiMAX PUSC-tile is an example of a group of subcarrier;the minimum time allocation for a PUSC-tile corresponds to 3 OFDM symbolperiods. For an embodiment, the UL transmission occurs in a UL subframe.The maintaining of the allocations of the tiles to antennas during theUL transmission precludes introducing channel estimation errors due toaveraging at the base station over time intervals greater than theminimum time interval of the groups of allocated subcarriers during anUL transmission.

For embodiment, the groups of subcarriers are defined by WiMAX BandAdaptive Modulation and Coding (BAMC) bins. Other embodiments includethe groups of subcarriers being defined by a 3GPP (3^(rd) GenerationPartnership Program)-LTE (Long Term Evolution) physical resource blocks.

Although specific embodiments have been described and illustrated, theembodiments are not to be limited to the specific fauns or arrangementsof parts so described and illustrated.

1. A method of a subscriber station transceiver allocating andtransmitting groups of subcarriers between a plurality of transceiverantennas, comprising: the subscriber station transceiver receiving atleast one downlink signal through each of the plurality of subscriberstation antennas; the subscriber station transceiver characterizing areceived signal of the at least one downlink signal over multiplesubcarriers; the subscriber station transceiver allocating groups ofsubcarriers for uplink transmission through each of the plurality ofsubscriber antennas, wherein the allocation is based on thecharacterized received signal of the at least one downlink signal overmultiple subcarriers.
 2. The method of claim 1, wherein characterizing areceive signal comprises characterizing a received signal power of thereceive signal.
 3. The method of claim 2, wherein allocating groups ofsubcarriers comprises allocating the subcarriers based on the receivedsignal power.
 4. The method of claim 1, wherein allocating groups ofsubcarriers for uplink transmission through each of the plurality ofsubscriber antennas, comprises allocating the groups based on anexpected uplink channel quality as estimated based on the characterizedreceived signals of the at least one downlink signal over multiplesubcarriers.
 5. The method of claim 4, wherein the expected uplinkchannel quality comprises at least one of an expected uplink capacity,an expected uplink signal to noise ratio, expected uplink total receivedsignal power.
 6. The method of claim 4, wherein the expected uplinkchannel quality comprises at least one of an estimated downlinkcapacity, an estimated downlink received signal power, an estimateddownlink received signal-to-noise ratio.
 7. The method of claim 1,wherein allocating groups of subcarriers comprises allocating based onat least one of a sum of receive signal powers across the plurality ofsubscriber station antennas, a sum signal-to-noise ratios across theplurality of subscriber antennas, a weighted sum of signal-to-noiseratios across the plurality of subscriber antennas.
 8. The method ofclaim 1, wherein the subscriber station transceiver characterizing thereceived downlink signals is based on a plurality of subcarriers.
 9. Themethod of claim 1, wherein the subscriber station transceivercharacterizing a received signal power of the at least one downlinksignal over multiple subcarriers comprises characterizing pilot tones ofa preamble of a downlink sub-frame of the at least one downlink signal.10. The method of claim 9, wherein the subscriber station transceivercharacterizing the pilot tones of the preamble is based on subcarriersof the preamble corresponding to the group of subcarriers to beallocated on the uplink.
 11. The method of claim 1, wherein thesubscriber characterizing the received signal of the at least onedownlink signal over multiple subcarriers occurs over a range ofsubcarriers that overlap the group of subcarriers to be allocated on theuplink.
 12. The method of claim 1, wherein the subscriber characterizingthe received signal of the at least one downlink signal includes asingle subcarrier that occurs within the range of subcarriers as thegroup of subcarriers to be allocated on the uplink.
 13. The method ofclaim 1, wherein the subscriber characterizing the downlink receivedsignals includes characterizations of downlink signals over a pluralityof frames.
 14. The method of claim 1, wherein allocating groups ofsubcarriers for uplink transmission through each of the plurality ofsubscriber antennas comprises allocating groups of subcarriers to basedon downlink channel quality metrics subject to meeting transmit powerconstraints of the subscriber station transceiver.
 15. The method ofclaim 1, wherein allocating groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennascomprises sorting a difference of vector downlink channel qualitymetrics from the plurality of subscriber station antennas.
 16. Themethod of claim 15, wherein allocating groups of subcarriers for uplinktransmission through each of the plurality of subscriber antennasadditionally comprises: performing initial allocations based on thesorting of difference vector downlink channel quality metrics;determining a number of groups of subcarriers allocated to eachsubscriber antenna; and modifying the initial allocations of groups ofsubcarriers to meet transmit power constraints of the subscriber stationtransceiver while causing minimal change to the downlink quality metric.17. The method of claim 1, wherein the subscriber characterizing thereceived signal power of the downlink signals over multiple subcarrierscomprises filtering downlink channel estimates.
 18. The method of claim1, wherein allocating groups of subcarrier for uplink transmissionthrough each of the plurality of subscriber antennas comprisesallocating groups of subcarriers within at least one sub-channel. 19.The method of claim 1, wherein each the groups of subcarriers comprisespilot tones and data tones of multiple subcarriers over multiplemulti-carrier symbols.
 20. The method of claim 1, wherein the groups ofsubcarriers are defined by a Worldwide Interoperability for MicrowaveAccess (WiMAX) (UL (uplink) PUSC (Partial Usage of Subchannels).
 21. Themethod of claim 1, wherein the groups of subcarriers are defined by BandAdaptive Modulation and Coding (BAMC) bins.
 22. The method of claim 1,wherein the groups of subcarriers are defined by Long Term Evolution(LTE) physical resource blocks.
 23. The method of claim 1, whereincharacterizing the received downlink signals comprises determining arelative signal power difference between multiple subcarrier signalsreceived through each of the plurality of subscriber antennas.
 24. Themethod of claim 1, further comprising maintaining the allocations of thegroups of subcarriers for a time interval greater than a minimum timeinterval of the groups of allocated subcarriers during an ULtransmission.